Cellular communications systems continue to grow in popularity and have become an integral part of both personal and business communications. Cellular telephones allow users to place and receive voice calls most anywhere they travel. Moreover, as cellular telephone technology has increased, so too has the functionality of cellular devices and the different types of devices available to users. For example, many cellular devices now incorporate personal digital assistant (PDA) features such as calendars, address books, task lists, etc. Moreover, such multi-function devices may also allow users to wirelessly send and receive electronic mail (email) messages and access the Internet via a cellular network and/or a wireless local area network (WLAN), for example.
Even so, as the functionality of cellular communications devices continues to increase, so too does the demand for smaller devices which are easier and more convenient for users to carry. One challenge this poses for cellular device manufacturers is designing antennas that provide desired operating characteristics within the relatively limited amount of space available for the antenna. This is particularly true where multi-frequency band operation is required. Some wireless communications devices use multiple antennas to cover multiple radio frequency (RF) bands. Thus, as the number of operating frequency bands increases, so to does the number of antennas that are required. As a result, it may not be possible to include all of the antennas required to provide operation in all desired frequency bands in some embodiments due to such space constraints.
When the number of operating frequency bands is fairly small, some conventional mobile wireless communications devices will use a single antenna to cover the frequency bands. Yet, in such devices it may be difficult to obtain a desirable match and antenna gain over all of the frequency bands, and some trade-offs may need to be made between the frequency bands.
One example of a single antenna system used for operating over multiple frequency bands is disclosed in U.S. Pat. No. 6,662,028 to Hayes et al. This patent is directed to a planar inverted-F antenna for communications devices, such as radiotelephones, that radiates within multiple frequency bands. Multiple signal feeds extend from a conductive element in respective spaced-apart locations. A respective plurality of micro-electromechanical system (MEMS) switches are electrically connected to the signal feeds and are configured to selectively connect the respective signal feeds to ground or RF circuitry. In addition, each MEMS switch can be opened to electrically isolate a respective signal feed.
Such antennas may be advantageous for operating over different frequency bands at different times, and over a relatively small range of operating frequencies. Nonetheless, there may be applications in which it is desirable to provide multi-frequency operation at the same time and over a fairly large range of frequencies but while still providing a relatively compact antenna configuration suitable for use in handheld wireless communications devices.